Platelet-rich plasma: ready or not?

Abstract

Surgeons are continually searching for ways to improve the success of bone grafting with either autogenous bone or other bone substitutes. Platelet-rich plasma (PRP) was first introduced to the oral surgery community by Whitman et al1 in their 1997 article entitled “Platelet Gel: An Autologous Alternative to Fibrin Glue With Applications in Oral and Maxillofacial Surgery.” The authors thought that “through activation of the platelets within the gel and the resultant release of. . .growth factors, enhanced wound healing should be expected.” PRP enjoyed a great increase in popularity in the oral and maxillofacial surgery community after the publication of a landmark article by Marx et al 2 in 1998. Marx et al’s study showed that combining PRP with autogenous bone in mandibular continuity defects resulted in significantly faster radiographic maturation and a histomorphometrically denser bone regenerate. It certainly seemed as though a new age in bone grafting had begun. The theory behind the use of PRP is compelling. It is now well known that platelets have many functions beyond that of simple hemostasis. Platelets contain important growth factors that, when secreted, are responsible for increasing cell mitosis, increasing collagen production, recruiting other cells to the site of injury, initiating vascular in-growth, and inducing cell differentiation. These are all crucial steps in early wound healing. Using the concept that if a few are good, then a lot may be better, increasing the concentration of platelets at a wound may promote more rapid and better healing. It seems very logical that increasing the concentration of platelets in a bone graft, and therefore increasing the concentration of growth factors, may lead to a more rapid and denser bone regenerate. The preparation of PRP is relatively simple. Blood collected from the patient undergoes a centrifugation process to concentrate the platelets. The platelets are concentrated into a small volume, which can then be added to a bone graft. When the platelet concentrate is activated, a gelatinous structure is formed and the important wound-healing growth factors are released. Platelets are known to contain a variety of growth factors, including transforming growth factor- (TGF), vascular endothelial growth factor (VEGF), and platelet-derived growth factor (PDGF). These growth factors are released from the platelets when they are activated, secreted, or aggregated by collagen or epinephrine. 3 TGF- and PDGF improve soft tissue and bony wound healing and, when delivered exogenously, stimulate collagen production, improve wound strength, and initiate callus formation.4-6 VEGF is a powerful angiogenic growth factor with an important role in wound healing and vascularity. 7 If PRP can indeed support a faster and denser bone graft, then oral and maxillofacial reconstructive surgery would be taken to a new level. However, many aspects of this theory may or may not be true. This was eloquently articulated by Schmitz and Hollinger, in a letter to the editor, in which they questioned the actual isoforms and the biological actions of the various growth factors concentrated in PRP, and stated their opinion that “at this time, basic research does not strongly endorse the ability of PRP to promote healing.” 8